how much for a new engine? REALLY NEED HELP

[preston7]

this one's for my van. its an Mreg 1.7TD astra. yesterday i did something really really stupid. as i was going onto the motorway the oil light came on going round a roundabout, but i was in a rush and was only going a few junctions down so i risked it and thrashed it, wen i came off i realised id shagged the engine. it was noisy so i got someone to bring me some oil, i dont think it was that bad at that point and am i right in thinking that the turbo would be the first to go?
To make things worse and i really regret this, i still drove the van for short distances until it was towed away. i now realise i might have done 10 miles
could i have seriosly fcuked the engine (bottom end damage?) how much should i pay for a new one?
also my engine fan now comes on wen you swich the ignition on and its really loud even after the engine had been left for over two hours it came on any one know why?

[2ltr 8v]

the oil light is a warning to tell you the oil is getting low, for you to top it up, like petrol gauge, you can leave it a bit before topping it up but it is wise to fill it asap.
And then thrashing it wouldn't of helped at all, so could of used alot more of what was left, try an oil change??

[16vmanta]

They are quite numb. I knocked the sump of my MK2 Astra 1.7DA on Fountains Earth, which is miles away from the nearest road. I drove for at least a half hour with a massive hole next to the oil pump. Got to a road and got some oil from a mate. Did at least 2 miles before the light was back on. Then did another 10 to his house. Swapped sump pans and did another 100K miles. I was so impressed and was gutted to eventually let it go.